An air disperser must be included in a spray dryer in order to obtain a more uniform drying of the liquid to be atomized. The drying air is brought into contact with the liquid to be atomized through a pipe equipped with one or more nozzles through which the liquid is streaming. The drying air is entering the pipe from the air disperser. Hence, it is the aim to obtain a uniform distribution of drying air in the air disperser in order to obtain a uniform and symmetrical downward flow of drying air in the pipe and further into the drying chamber of the spray dryer.
In the air dispersers known today it may be difficult to obtain a uniform and symmetrical flow of the drying air. These difficulties are most often due to the construction upstream of the supply pipe for the drying air, but may also be due to the design of the air disperser. If the drying air is not uniformly distributed in the air disperser, then neither the flow of drying air will be uniformly distributed at the point where the drying air and the liquid to be atomized are brought together. Consequently, a non-uniform drying process will be performed resulting in for example formation of deposits on the wall inside of the drying chamber, production of a product of less quality and a reduced capacity.
For many years it has been known to incorporate guide vanes in air dispersers in order to improve the distribution of drying air inside of the air disperser. For example in U.S. Pat. No. 4,227,896 (Niro) a gas distribution device for the supply of a processing gas to an atomizing chamber is described, said device containing two vane sets positioned opposite to each other in order to obtain a more uniform downwards directed flow of the drying air. However, this design aims at a rotational flow.
As an alternative solution perforated plates have been introduced in such air dispersers in order to avoid turbulence in the air flow and hence to obtain a more uniform distribution of the air (see for example FR 1.289.817 (Niro)). However, the use of such perforated plates have shown to cause difficulties in respect of keeping the perforated plates clean. Especially, when the spray dryer is to be used in the food or pharmaceutical industry the sanitary aspects of the production design are very important.